Field of the Invention
The present invention relates to a process for production of a porous ceramic article. The ceramic article according to the present invention is useful as an implant material for an artificial bone, a prosthetic bone, a filter medium and so on.
Description of the Related Art
A porous ceramic article is used as a ceramic implant material for an artificial dental root, an artificial bone and so one, and the material replaces the hard tissue of the human body since it is excellent in biological compatibility and mechanical strength.
When a bone contacts a porous material having pores of more than 50 .mu.m in diameter, a newly formed bone cell invades the pore. The porous material having such a larger diameter is poor in the mechanical strength. To overcome this problem, a process for the production of a prosthetic bone article in which a porous material is combined with a metal or dense ceramic material is proposed in Japanese Patent Kokai Publication No. 109407/1974 (hereinafter referred to as "reference 1"). This process comprises heating a ceramic material in the form of granules having a selected size at a temperature lower than a sintering temperature thereof, compressing it under a pressure of about 1 ton/cm.sup.2 and sintering to form a porous block. When combined with the metal, the process further comprises disposing the sintered block in a mold and casting the metal to fix the block to a metal rod. When combined with the ceramic material, the process further comprises compressing together the block which has not been sintered and the dense ceramic material in the form of a block produced in a separate step and then sintering to make them integral. It is reported that a radius of the pore of the porous block is in the range of from 100 to 200 .mu.m and its porosity is 30%. Another process is described in Japanese Utility Model Publication No. 34731/1981 (hereinafter referred to as "reference 2"), in which an implant article for the use in a bone is produced by fixing porous alumina ceramic material around a core rod of single crystalline alumina. This process comprises mixing together ceramic powder and material which may be burnt off, compression molding and then calcining to produce a porous material, which is fixed around an outer shell of a core made of the single crystalline alumina with an adhesive or by screwing. It is reported that a diameter of the pore of the porous material is in the range of 0.2 to 0.7 mm.
In the process described in the reference 1, the compressed block made of the alumina granules having a diameter of in the range of 0.5 to 1.5 mm is heated at a temperature lower than the sintering temperature and then sintered to produce the porous material. Therefore, it is required to prepare the alumina granules having a diameter in the range of from 0.5 to 1.5 mm and to pre-sinter the alumina granules. Further, the process is not suitable to produce a porous material of a larger size or a complicated shape since the compression pressure should be in the range from 1 to 4 tons/cm.sup.2.
In the process described in the reference 2, the ceramic powder and the material which may be burnt off are mixed and compression molded together and then sintered into the porous material. Thus, it is impossible to selectively form the pores into a closed cell structure or an open cell structure, or to control sizes or directions of the pores since the position of the burnt-off material in the compressed material cannot be controlled.